This invention relates to electrical resistance heaters, and more particularly to open coil heaters in which the heating element is formed of electrical resistance heating wire, of Nichrome or the like, and even more particularly in which the heating element is formed in a helical coil and is exposed to the air. The heating element is supported on a frame or the like by using ceramic-type insulators. Such heaters find a wide range of applications, for example, in electric clothes dryers, resistance heating systems for residential and in commercial heating and ventilating systems.
Open coil heaters have typically utilized two types of ceramic (steatite) insulators to support the heating coil on an open heater frame. As shown in prior U.S. Pat. Nos. as 1,154,417, 2,478,808, 2,478,809, 2,567,547, 2,730,603 and 3,016,441, and in Canadian Patent 554,732 bushing-type insulators having a central opening therethrough to receive the entire heater coil. The insulator, in turn, is supported on the heater frame by a metal strap, wire, or rod wrapped around the insulator and received in notches or a groove formed on the insulator. The support wire is welded to the heater frame. This manner of mounting the insulator has become known as "wire wrap" heater construction.
As shown in the co-assigned U.S. Pat. Nos. 3,846,619, Des. 248,943, 4,250,399, Des. 262,285, 4,472,624, and U.S. Pat. Nos. 4,268,742, 4,531,017, 4,617,547, 4,628,190 and 4,692,599 and in British Patent 1,003,610, another type of ceramic insulator, referred to as a "point suspension" type insulator, also came into use. These "point suspension" insulators have a variety of notches or slots which grip the heater coil at a point, rather than requiring the heater coil to be entirely inserted through the central opening of a bushing type insulator. This point suspension method of supporting a heater coil on an insulator facilitates ease of assembly of the heater (because the insulator does not have to be inserted through a series of bushing insulators) and results in cooler operation and a longer service life of the heater coil (because of better heat dissipation).
Such "point suspension" type open coil heating elements have been mounted on a heater frame in a variety of ways. As shown in the above mentioned U.S. Pat. Nos. 4,486,619, 4,250,399 and 4,268,472, the insulators are provided with apertures or grooves which receive a metal tab from an insulator support bar bent into the aperture or groove to hold the insulator on the heater frame. Further, as shown in British patent 1,003,610 and in U.S. Pat. Nos. 4,531,017 and 4,692,599, the previously discussed "wire wrap" support method can also be utilized to mount "point suspension" insulators on a heater frame. As shown in U.S. Pat. No. 4,472,624, point suspension insulators have been "twist lock" mounted in a sheet metal strap or bar having openings which allow the insulator to be readily inserted into the opening and then turned 90.degree. to be locked into place.
Generally, the tab locked-in-place insulators, as shown in U.S. Pat. No. 4,250,339, are used in applications in which the generally flat point suspension insulator was oriented generally perpendicular to the axis of the heater coil. Wire wrap mounted point suspension insulators offer an inexpensive way to mount point suspension insulators in a wide range of applications. In other applications in which the point suspension insulator is oriented in line with the axis of the heater coil, wire wrap clips are used to mount the insulators on the heater frame. However, the insulators oftentimes tended to be loose within their wire wrap clips. In certain instances, this results in objectionable rattling noises emanating from the insulators which rattle within their wire wrap support clips during operation of an appliance (e.g., a clothes dryer) in which the heater is installed.
There is a need for a method of mounting point suspension insulators which combine the low cost and flexible design features of prior wire wrapped mounting techniques combined with the secure mounting of the insulators afforded by the bent tabbed mounting method.